1. Field of the Invention
The invention relates to a dispenser for supplying small amounts of a pasty substance, e.g. adhesive or solder paste, onto printed circuit boards and for surface mounting of electronic components.
2. Prior Art
German printed application 37 28 054 teaches an apparatus and a method for metering and dispensing small amounts of a pasty substance of the kind mentioned above. Thereby a cartridge filled with the adhesive or the solder paste is used. In the cartridge a plunger is arranged, onto which compressed air can be submitted. The cartridge exhibits a hollow needle through which the pasty substance flows when being applied onto a printed circuit board. The cartridge is surrounded on its outside with a heater in the form of a heating coil to keep the cartridge at a desired, constant temperature.
In the known device the complete cartridge has to be exchanged if the supply of pasty substance is consumed. Contrary to this, in an apparatus according to the invention, the pasty substance is supplied to a dispenser from a supply vessel which may be a cartridge. Only a very small amount of the pasty substance is in the dispenser. The dispenser is used only to dispense portions of the pasty substance; storage of the pasty substance takes place outside of the dispenser. Compared with a filled cartridge according to the state of the art, a dispenser according to the invention is lighter and smaller, its mass does not change with filling height, and it can be continuously supplied with pasty substance thereby avoiding work interruptions in order to replace an empty cartridge.
A dispenser of the kind mentioned above is described in the published German application 39 35 709 of the applicant. The dispenser described there has no means for controlling the temperature. Furthermore, the amount of pasty substance ejected is substantially determined by the pressure acting on the pasty substance, by the flow characteristics of the pasty substance and the time duration that the valve needle is lifted from the valve face.